1. Field of the Invention
This invention relates to a rotor construction of a gas turbine, and more particularly to a gas turbine rotor which can achieve a high-efficiency and large-output design of the gas turbine.
2. Description of the Related Art
A configuration of a conventional rotary disk, used in a gas turbine, is based on an idea of such a design that a hub portion, defining an abutment surface for contact with an adjacent disk, is formed on each side of a disk in the form of an equal-stress disk in which stresses, developing at radial positions, are equal or uniform in the entire radial direction.
Recently, however, in gas turbine facilities, the system has been required to have a high-efficiency in order to save energy and also to protect the environment. One method of achieving such a high-efficiency design is to increase a turbine inlet temperature.
Also, with an increased demand for electric power and particularly with the increase of peak electric power, a gas turbine has been required to produce a large output. One method of achieving such a large-output design is to increase an annular cross-sectional area of a gas flow passage.
With the increase of the turbine inlet temperature, an environmental temperature, to which the rotary disks are exposed, increases. Generally, the strength of a material of which the rotary disks are made is lowered with the increase of the environmental temperature. Therefore, it is necessary to increase the thickness of the rotary disks so as to reduce a developed stress, thereby compensating for the lowered strength of the material.
The increase of the annular cross-sectional area of the gas flow passage invites the increase of a centrifugal force acting on blades, and as a result a stress, developing at a central portion of the rotary disk, increases, and therefore in this case, also, the thickness of the rotary disk need to be increased in order to reduce a developed stress.
As shown in FIG. 8, a conventional gas turbine, in which a gas turbine rotor of the type described is used, broadly comprises a compressor portion 100, a combustor portion 200, and a turbine portion 300. In this gas turbine, the air, drawn from the atmosphere, is compressed in the compressor 100, and in the combustor portion 200, the thus compressed air is mixed with fuel and is burned, thereby producing combustion gas of high temperature and pressure. The thus produced combustion gas is expanded in the turbine portion 300 to produce power, and then is discharged as exhaust gas to the atmosphere. Part of the power, produced in the turbine portion 300, is used to drive the compressor portion 100, and the remainder of the power other than the power used to drive a compressor of the compressor portion 100 serves as driving power for the gas turbine, and a generator (not shown) is driven by this driving power of the gas turbine.
In order to deal with the above increased-thickness problem, there has been proposed a gas turbine rotor of such a gas turbine having the construction shown in FIG. 9. FIG. 9 is a cross-sectional view showing the construction of a turbine portion of a gas turbine V84.3 of Siemens made public at Yokohama International Gas Turbine Institute (1995). More specifically, FIG. 9 is a cross-sectional view of a stacked rotor in which disks, each having a plurality of moving blades fitted therein, are stacked together in a multi-stage manner in a direction of a rotational axis, and a left side is an upstream earlier-stage side while a right side is a downstream later-stage side. In FIG. 9, reference numeral 1 denotes the disk, reference numeral 2 the moving blade, reference numeral 3 a stacking bolt, reference numeral 4 a stationary blade, and reference numeral 5 a shroud. The disks 1 are stacked and fastened together by the stacking bolt. 3 passing through holes formed respectively through central portions of the disks 1.
In order to suppress a large centrifugal stress, produced at the central portion of the rotary disk 1 of FIG. 9 in accordance with centrifugal forces acting on the moving blades 2 and the outer peripheral portion of the disk, to within an allowable range, and also to compensate for the lowered strength of the disk material due to the increase of the environmental temperature, the rotary disk 1, shown in FIG. 9, is increasing in thickness continuously (progressively) toward the central portion thereof, and is increased in thickness at its innermost peripheral portion as much as possible so that the rotary disk 1 almost contacts the adjacent rotary disks 1 at their innermost peripheral portion.
It is expected that gas turbines are required to achieve a higher efficiency and a larger output, and to meet these requirements, if the thickness of the inner peripheral portion of each rotary disk is increased as proposed in the prior art technique, it is possible that the adjacent rotary disks contact each other at their inner peripheral portions, and therefore this method of increasing the thickness of the rotary disk is limited. A surface of a circular hole or opening (hereinafter referred to as "inner hole"), formed through the central portion of the rotary disk, is pulled radially outwardly at its central portion to a larger degree by the tensile centrifugal forces acting on the outer peripheral portion of the disk and the moving blades. Therefore, there occurs the large difference in radial deformation between the central portion of the surface of the central hole and the opposite (right and left) side portions of the surface of the central hole, and the correspondent stress component in the vicinity of the central portion of the surface of the inner hole locally increases since compressive stress components in the direction of the thickness of the rotary disk act on this central portion. Thus, there has been encountered a problem that merely by increasing the thickness of the inner peripheral portion of the rotary disk, this localized peak correspondent stress can not be reduced satisfactorily.